1. Field of the Invention
This invention relates to a developer-carrying member used in developing apparatus of an electrophotographic system, which constitutes image-forming apparatus such as copying machines and laser beam printers, and more particularly to a developer-carrying member having on its surface a conductive resin coating layer. It also relates to a process for producing such a developer-carrying member, a developing apparatus having the developer-carrying member, and an image-forming apparatus having such a developing apparatus.
2. Related Background Art
As a developing apparatus in which electrostatic latent images formed on the surface of a photosensitive drum serving as an image bearing member are developed using a magnetic toner of a one-component developer, conventionally known is an apparatus in which triboelectric charges with a polarity reverse to that of electric charges of an electrostatic latent image on the photosensitive drum and that of development reference potential are imparted to magnetic toner particles by the friction between magnetic toner particles themselves and mutual friction between a developer sleeve as a developer-carrying member and the magnetic toner particles, the magnetic toner thus charged is very thinly coated on the developer sleeve and is carried and transported to a developing zone where the developer sleeve faces the photosensitive drum, and in that developing zone the magnetic toner is caused to fly and adhere to the electrostatic latent image on the photosensitive drum surface by the action of a magnetic field generated by a magnet disposed stationarily inside the developer sleeve, to make development to render the electrostatic latent image visible as a toner image.
As the developer-carrying member used in such an apparatus, commonly in wide used are members obtained by forming a metal such as aluminum, nickel, corrosion-resistant steel (stainless steel) or an alloy or compound thereof into a cylindrical shape and treating its surface by, e.g., electrolysis, blasting or filing so as to have a stated surface roughness. In particular, aluminum alloys are inexpensive compared with other metals and moreover have so high a thermal conductivity as to little cause any thermal deformation, and also may hardly cause developer""s charge-up. Accordingly, developer-carrying members making use of aluminum alloys have become prevalent.
However, aluminum sleeves making use of such aluminum alloys have a low hardness, and hence they have a problem that the sleeve surface so treated by blasting as to have a stated surface roughness may easily wear at the initial stage of service when left as it is. Hence, as disclosed in Japanese Patent Application Laid-Open No. 1-276174, it is attempted to use a cylinder formed of an aluminum alloy and coated with a resin on its surface. In such an example, the sleeve surface is coated with a phenolic resin having a good mechanical strength, to form a conductive resin layer in which conductive particles such as carbon or graphite particles stand dispersed in the resin, thereby improving its surface hardness while maintaining conductivity necessary for the developer-carrying member. In such a case, the sleeve surface is coated with the resin by spraying in a thickness of about 10 to 20 xcexcm, and hence can fundamentally be flat though the unevenness the underlying aluminum alloy surface has is slightly followed. However, its surface is in such a state that fine particles such as carbon or graphite particles have been embedded in the phenolic resin, and hence the cross-sectional shape of the roughness stands relatively close to the above blasted metal surface.
When a positively chargeable toner is triboelectrically charged and when a coating film is formed using the phenolic resin as stated above, the resin has originally such a charge polarity that it charges the toner negatively. Hence, it is hard for the toner to be positively charged. Accordingly, in usual instances, a positive-charge-providing molecule such as a quaternary ammonium salt is added to the resin so that the positively chargeable toner (developer) can be provided with positive charges. However, a sufficient charge quantity can not yet be attained, and there has been a problem that, when the developer-carrying member having a conductive resin layer is used, images formed have a low image density. This tendency is remarkable especially at the initial stage of the driving of image-forming apparatus.
An object of the present invention is to provide a developer-carrying member that can solve the above problem, a developer-carrying member production process that can produce such a developer-carrying member, a developing apparatus having the developer-carrying member, and an image-forming apparatus having such a developing apparatus.
Another object of the present invention is to provide a developer-carrying member that can be improved in its ability to impart electric charges triboelectrically to positively chargeable developers, and provide a developer-carrying member production process that can produce such a developer-carrying member with ease, a developing apparatus having the developer-carrying member, and an image-forming apparatus having such a developing apparatus.
Still another object of the present invention is to provide a developer-carrying member by which positively chargeable one-component developers can stably triboelectrically be charged and can keep image density from changing not only at the initial stage of service after the developer-carrying member has been produced but also at a stage where its conductive resin coating layer has worn as a result of long-term service, and provide a developer-carrying member production process that can produce such a developer-carrying member with ease, a developing apparatus having the developer-carrying member, and an image-forming apparatus having such a developing apparatus.
A further object of the present invention is to provide a developer-carrying member production process by which particles of graphite or molybdenum disulfide having good positive-charge-providing properties can effectively be laid bare or uncovered to the surface of the developer-carrying member in order to obtain a developer-carrying member that enables triboelectric charging of positively chargeable one-component developers sufficiently and without changes, and to prevent initial-stage image density from decreasing.
To achieve the above objects, the present invention provides a developer-carrying member comprising a conductive substrate and a conductive resin coating layer provided on the surface of the conductive substrate, wherein;
the conductive resin coating layer comprises a resin in which graphite particles stand dispersed, and the graphite particles are uncovered to the surface of the conductive resin coating layer at a degree of uncovering of 50% or more.
The present invention also provides a developer-carrying member comprising a conductive substrate and a conductive resin coating layer provided on the surface of the conductive substrate, wherein;
the conductive resin coating layer comprises a resin in which molybdenum disulfide particles stand dispersed, and the molybdenum disulfide particles are uncovered to the surface of the conductive resin coating layer at a degree of uncovering of 30% or more.
The present invention still also provides a process for producing a developer-carrying member, comprising the steps of:
primary treatment to form on the surface of a conductive substrate a conductive resin coating layer comprising a resin in which graphite particles stand dispersed; and
secondary treatment to remove a surface portion of the conductive resin coating layer to uncover the graphite particles to the surface of the conductive resin coating layer at a degree of uncovering of 50% or more.
The present invention further provides a process for producing a developer-carrying member, comprising the steps of:
primary treatment to form on the surface of a conductive substrate a conductive resin coating layer comprising a resin in which molybdenum disulfide particles stand dispersed; and
secondary treatment to remove a surface portion of the conductive resin coating layer to uncover the molybdenum disulfide particles to the surface of the conductive resin coating layer at a degree of uncovering of 30% or more.
The present invention still further provides a developing apparatus comprising:
a positively chargeable one-component developer for developing an electrostatic latent image formed on an image-bearing member; and
a developer-carrying member for carrying thereon the positively chargeable one-component developer;
the developer-carrying member comprising a conductive substrate and a conductive resin coating layer provided on the surface of the conductive substrate, wherein;
the conductive resin coating layer comprises a resin in which graphite particles stand dispersed, and the graphite particles are uncovered to the surface of the conductive resin coating layer at a degree of uncovering of 50% or more.
The present invention still further provides a developing apparatus comprising:
a positively chargeable one-component developer for developing an electrostatic latent image formed on an image-bearing member; and
a developer-carrying member for carrying thereon the positively chargeable one-component developer;
the developer-carrying member comprising a conductive substrate and a conductive resin coating layer provided on the surface of the conductive substrate, wherein;
the conductive resin coating layer comprises a resin in which molybdenum disulfide particles stand dispersed, and the molybdenum disulfide particles are uncovered to the surface of the conductive resin coating layer at a degree of uncovering of 30% or more.
The present invention still further provides an image-forming apparatus comprising a developing apparatus having:
a positively chargeable one-component developer for developing an electrostatic latent image formed on an image-bearing member; and
a developer-carrying member for carrying thereon the positively chargeable one-component developer;
the developer-carrying member comprising a conductive substrate and a conductive resin coating layer provided on the surface of the conductive substrate, wherein;
the conductive resin coating layer comprises a resin in which graphite particles stand dispersed, and the graphite particles are uncovered to the surface of the conductive resin coating layer at a degree of uncovering of 50% or more.
The present invention still further provides an image-forming apparatus comprising a developing apparatus having:
a positively chargeable one-component developer for developing an electrostatic latent image formed on an image-bearing member; and
a developer-carrying member for carrying thereon the positively chargeable one-component developer;
the developer-carrying member comprising a conductive substrate and a conductive resin coating layer provided on the surface of the conductive substrate, wherein;
the conductive resin coating layer comprises a resin in which molybdenum disulfide particles stand dispersed, and the molybdenum disulfide particles are uncovered to the surface of the conductive resin coating layer at a degree of uncovering of 30% or more.